Method for making ultra-narrow read sensor and read transducer device resulting therefrom

ABSTRACT

Disclosed are methods for making ultra-narrow track width (TW) read sensors, and read transducers incorporating such sensors. The methods utilize side-wall line patterning techniques to prepare ultra-narrow mill masks that can be used to prepare the ultra-narrow read sensors.

RELATED CASES

This application is a continuation of U.S. patent application Ser. No.13/929,633 (Atty. Docket No. F5722) filed on Jun. 27, 2013, which claimsthe benefit of U.S. Provisional Application Ser. No. 61/835,913 (Atty.Docket No. F5722.P) filed Jun. 17, 2013, the contents of which arehereby incorporated herein by reference in their entireties.

TECHNICAL FIELD

This disclosure relates to the field of read sensors, and their methodsof manufacture.

BACKGROUND

Computer hard drives store data by affecting the magnetic field ofmemory cells on a hard drive disk. The stored data is read by passing aread head sensor above a memory cell to respond to, and thus detect, theorientation of the magnetic field in the memory cell. The smaller thememory cells on the hard drive disk, the more densely they can bepacked, increasing the density of data storage possible on a hard drivedisk.

However, making smaller memory cells is not all that is required toincrease data density storage capacity. Increasingly smaller memorycells require increasingly smaller read sensors, particularly readsensors with a narrow track width, in order to be responsive to themagnetic field of a single memory cell.

Currently there is no commercial lithography tool than can provide readsensors with line widths less than about 30 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

The present application is illustrated by way of example, and notlimitation, in the figures of the accompanying drawings in which:

FIG. 1 illustrates steps in an exemplary method for preparing anultra-narrow mill mask using a side-wall line deposition technique.

FIG. 2 is a SEM image of a side-wall structure formed as a intermediatestructure during the exemplary method shown in FIG. 1.

FIG. 3 is a SEM image of a side-wall line structure formed as aintermediate structure during the exemplary method shown in FIG. 1.

FIG. 4 is a SEM image of an ultra-narrow mill mask formed from theexemplary method shown in FIG. 1.

FIGS. 5A and 5B are SEM images of two alumina mill masks (at about 10 nmand 18 nm thick, respectively) prepared according to one exemplarymethod.

FIG. 6 is a contour plot showing critical dimension uniformity of linestructures prepared according to an exemplary method.

FIG. 7 illustrates steps for preparing an ultra-narrow read sensor usingan ultra-narrow mill mask according to one exemplary method.

FIG. 8 is a SEM image of an alumina mill mask remaining above a SiCultra-narrow line structure prepared as an intermediate step in theexemplary method seen in FIG. 7.

FIGS. 9A and 9B are SEM images of two SiC ultra-narrow line structures(at about 10 nm and 18 nm thick, respectively) prepared as anintermediate step in the exemplary method seen in FIG. 7.

FIG. 10 is a SEM image of a ultra-narrow reader junction preparedaccording to the exemplary method seen in FIG. 7.

FIG. 11 illustrates steps for preparing an ultra-narrow read sensorusing an ultra-narrow mill mask according to another exemplary method.

FIG. 12 is a SEM image of a ultra-narrow reader junction preparedaccording to the exemplary method seen in FIG. 11.

DETAILED DESCRIPTION

Disclosed are methods for making ultra-narrow track width (TW) readsensors and read transducers incorporating such sensors. The methodsutilize side-wall line patterning techniques to prepare ultra-narrowmill masks that can be used to prepare the read sensors.

In the following description, numerous specific details are set forth toprovide a thorough understanding of various embodiment of the presentinvention. It will be apparent however, to one skilled in the art thatthese specific details need not be employed to practice variousembodiments of the present invention. In other instances, well knowncomponents or methods have not been described in detail to avoidunnecessarily obscuring various embodiments of the present invention.

As used herein, the phrase “ultra-narrow” refers to a dimension on theorder of less than about 35 nm; such as between about 3 and 35 nm; suchas between about 5 and 30 nm; such as between about 5 and 25 nm; such asbetween about 5 and 20 nm; such as between about 7 and 18 nm; or betweenabout 5 and 10 nm; such as between about 5 and 7 nm; or between about 10and 18 nm.

Currently there is no commercial lithography tool than can provide 10-20nm linewidth structures. Described herein are side-wall line patterningtechniques that are capable of delivering ultra-narrow linewidthstructures. In particular, the side-wall line patterning techniquesdescribed herein are capable of delivering well defined linewidthscontrolled by thickness of a conformally deposited material. Inparticular, the conformally deposited material may be applied via anatomic layer deposition technique or the like, which allows forcontrolled deposition across a wide range of thicknesses as needed fordesired reader design and fabrication requirements. Further, in someembodiments, the conformally deposited material is deposited under suchconditions as to provide a high degree of CD uniformity. When depositedso as to provide a coating on a side-wall of a layered structure, theresulting coated structure can be further processed according toappropriate etching chemistries known in the art to provide anultra-narrow mill mask on a substrate, which allows for furtherpatterning so as to prepare an ultra-narrow reader junction for use in aread sensor.

An exemplary embodiment of a side-wall patterning technique usable todeliver linewidth structures is shown in FIG. 1. As seen in FIG. 1, theside-wall line patterning techniques may comprise deposition of one ormore sacrificial layers above a substrate, where each sacrificial layercomprises a material that is susceptible to an etching chemistry, suchas a reactive ion etching chemistry.

As will be understood by one of skill in the art, any suitabledeposition technique, including vapor deposition, may be used dependingon the desired composition of the one or more sacrificial layers. Insome embodiments, the one or more sacrificial layers comprises a layerof amorphous carbon. In such embodiments, the amorphous carbon may bedeposited by vapor deposition. Various thicknesses of the amorphouscarbon layer may be used. In some embodiments, the thickness is lessthan or equal to about 100 nm thick. In addition, or in the alternative,the one or more sacrificial layers comprises a layer of tantalum. Likeamorphous carbon, tantalum may also be deposited by vapor deposition.Again, various thicknesses may be used, such as less than or equal toabout 40 nm. In some embodiments, the one or more sacrificial layers maycomprise a plurality of sacrificial layers. In one particular exemplaryembodiment, the one or more sacrificial layers comprise a tantalum layeron top of an amorphous carbon layer.

In some embodiments, a masking layer is applied to at least a portion ofthe uppermost sacrificial layer after the one or more sacrificial layersare in place. The masking layer may comprise a material that is notsusceptible to the same reactive ion etching chemistry as the uppermostsacrificial layer. In some embodiments, the masking layer is applied asa photoresist pattern leaving at a portion of the uppermost sacrificiallayer exposed. The masking layer may be applied such that an edge of themasking layer defines a straight line along an exposed portion of theuppermost sacrificial layer.

An intermediate structure prepared according to such a method is shownas the starting point of sequence in FIG. 1. The initial structurecomprises a substrate 1, two sacrificial layers 2 and 3, and a maskinglayer 4.

Once the masking layer 4 is in place, the layered structure is subjectedto reactive ion etching chemistries selected to etch the exposed portionof the sacrificial layers. The masking layer protects the coveredportion of the sacrificial layers, thereby creating a vertical side-wallstructure defined by the sacrificial layer materials. In the exemplarymethod shown in FIG. 1, the masking layer 4 is then removed, exposing ahorizontal surface of the uppermost sacrificial layer, and leading tothe layered structure seen between steps A and B. A SEM image of such anexemplary intermediate layered structure is also seen in FIG. 2.

A material capable of conformal deposition is then applied to layeredstructure, coating the horizontal and vertical surfaces. As used herein,a material capable of “conformal” deposition is a material that isdeposited as a coating with substantially even thickness, regardless ofthe orientation of the surfaces it is being deposited on. In thisregard, substantially even thickness means that the variation betweensurface thickness is less than or equal to about 10%, such as less thanor equal to about 5%, such as less than or equal to about 2%, regardlessof surface orientation. In some embodiments, this conformally depositedmaterial is not susceptible to the same reactive ion etching chemistryas at least one of the sacrificial layers. In the exemplary method shownin FIG. 1, the conformally deposited layer 5 applied in step B.

In some embodiments, the conformally deposited material is applied viaatomic layer deposition. In some embodiments, the conformally depositedmaterial comprises alumina (i.e. aluminum oxide). However, it is notintended that the methods described herein are limited to any particularconformally deposited material being applied by any particular fashion.As described above, it is sufficient that the material is capable ofbeing conformally deposited at a desired thickness, and that thematerial is not susceptible to the same reactive ion etching chemistryas at least one of the sacrificial layers.

Once the material has been conformally deposited, the deposited materialcovering a horizontal surface of the uppermost sacrificial layer isremoved in a way that leaves at least a portion of the material coveringa vertical surface intact. This removal may be accomplished by anymethod known in the art, including a reactive ion etching specificallytargeted to the conformally deposited material. Removal of theconformally deposited material from a horizontal surface of theuppermost sacrificial layer, and subsequent removal of the uppermostsacrificial layer, is seen as step C in FIG. 1. A SEM image of such anexemplary intermediate structure with a side-wall coating is seen inFIG. 3.

What remains is at least one sacrificial layer defining a verticalside-wall that is coated with the conformally deposited material. Aswill be appreciated, the thickness of the side-wall coating isdetermined by the thickness of the initial conformal deposition. In thisregard, atomic layer deposition is particularly useful, as the thicknessof the deposited layer can by finely controlled, allowing for depositionof a layer of virtually any desired thickness, such as a thickness lessthan about 35 nm; such as between about 3 and 35 nm; such as betweenabout 5 and 30 nm; such as between about 5 and 25 nm; such as betweenabout 5 and 20 nm; such as between about 7 and 18 nm; or between about 5and 10 nm; such as between about 5 and 7 nm; or between about 10 and 18nm.

The remaining structure may then be subjected to reactive ion etchingspecifically directed to remove all remaining sacrificial layermaterial, leaving a ultra-narrow line structure that can be used toserve as a mill mask for further processing of the underlying substrate.This removal step is shown in FIG. 1 as step D, with the resultingultra-narrow mill mask 6 atop substrate 1. A SEM image of such anexemplary ultra-narrow mill mask atop a substrate is seen in FIG. 4.

Given the fact that the thickness of the conformal coating ultimatelydetermines the thickness of the mill mask, various embodiments of themethods described herein may be used to provide mill masks withultra-narrow critical dimension. For instance, SEM images of twoexemplary ultra-narrow mill masks produced by methods described hereinare shown in FIG. 5. The thicknesses of the shown ultra-narrow millmasks were measured to be about 10 nm (FIG. 5A) and 18 nm (FIG. 5B),although thinner mill masks have been produced.

An additional feature of some of the ultra-narrow mill masks produced bysome of the embodiments presented herein results from the consistentthickness that a conformal coating may be applied. That is, ultra-narrowmill masks produced by various embodiments of the methods describedherein may exhibit high critical dimension uniformity. For instance, aside-wall patterned mill mask may have a critical dimension uniformity(expressed as within wafer variation) of less than about 1 nm; such asless than about 0.75 nm; such as less than about 0.6 nm. An contour plotdemonstrating such critical dimension uniformity for a mill maskproduced according to one embodiment is seen in FIG. 6. Observed withinwafer variation (WIW sigma) for this example was about 0.58 nm.

Further, it is intended that a substrate may be any suitable material orstructure. In particular, a substrate may be a read sensor stackcomprising a plurality of layers. In such embodiments, a side-wallpatterned mill mask may be used to further process the substrate to makea read sensor with an ultra-narrow track width.

In some embodiments, a substrate comprises an uppermost layer comprisinga material that is susceptible to a reactive ion etching chemistry thatis different from any of the one or more sacrificial layers. Thisuppermost layer may be of any suitable thickness, which may be selectedbased on the chemical identity of the uppermost substrate layer. In someembodiments, the uppermost substrate layer comprises silicon carbide(SiC). If present as the uppermost substrate layer, silicon carbide maybe at any desired thickness, including a thickness of about 50 nm orless.

The substrate may further comprise an etch stop layer found directlybeneath the uppermost substrate layer. In such embodiments, the etchstop layer comprises a material that is not susceptible to the samereactive ion etching chemistry as the uppermost substrate layer. Again,this uppermost layer may be of any suitable thickness, which may beselected based on the chemical identity of the etch stop layer. In someembodiments, the etch stop layer may comprise a chromium layer; such asa chromium layer that is about 25 Å thick.

One exemplary method of processing a multilayered substrate into areader junction is seen in FIG. 7. The initial structure comprises amulti-layered substrate 1 comprising a base layer 7, an etch stop layer8, and an uppermost substrate layer 9. In the method shown in FIG. 7,the uppermost substrate layer 9 is subjected to a reactive ion etch soas to remove portions of the substrate layer 9 not protected by the millmask 6. The resulting line structure is a layered line structurecomprising the original mill mask above the protected portion of thesubstrate layer 9 (shown in FIG. 7 as the structure following step A). ASEM image of an exemplary layered line structure prepared according tothis method is shown in FIG. 8.

The original mill mask may then be removed, leaving a line structure 10formed of the uppermost substrate material, and with about the samethickness of the original mill mask. SEM images of two exemplary linestructures are seen in FIGS. 8A (about 10 nm thick) and 8B (about 18 nmthick). The remaining substrate and line structure may then be processedby techniques known in the art to form a reader junction with a trackwidth equal to about the thickness of the line structure 10. A SEM imageof an example of a reader junction prepared by this method is seen inFIG. 10.

Another exemplary method for further processing a reader stack substrateinto a reader junction is seen in FIG. 11. This exemplary method issimpler than that seen in FIG. 7 in that the side-wall line patternedmill mask 6 is used directly to pattern a reader junction 11. In theseembodiments, the substrate may comprise a tunneling magnetoresistive(TMR) surface. A SEM image of an example of a reader junction preparedby this method is seen in FIG. 12.

As such, methods described herein may be used to prepare read sensorscomprising a read junction track width of less than about 35 nm; such asbetween about 3 and 35 nm; such as between about 5 and 30 nm; such asbetween about 5 and 25 nm; such as between about 5 and 20 nm; such asbetween about 7 and 18 nm; or between about 5 and 10 nm; such as betweenabout 5 and 7 nm; or between about 10 and 18 nm. Similarly, these readsensors may be used to prepare transducers comprising read sensors witha read junction track width of less than about 35 nm; such as betweenabout 3 and 35 nm; such as between about 5 and 30 nm; such as betweenabout 5 and 25 nm; such as between about 5 and 20 nm; such as betweenabout 7 and 18 nm; or between about 5 and 10 nm; such as between about 5and 7 nm; or between about 10 and 18 nm.

In the foregoing specification, embodiments of the disclosure have beendescribed with reference to specific exemplary features thereof. Itwill, however, be evident that various modifications and changes may bemade thereto without departing from the broader spirit and scope of thedisclosure. The specification and figures are, accordingly, to beregarded in an illustrative rather than a restrictive sense.

That which is claimed is:
 1. An apparatus, comprising: a read sensorcomprising a patterned read sensor stack on a substrate, wherein theread sensor stack comprises a plurality of layers; and a mill mask abovethe read sensor stack, wherein the mill mask is a line structuredeposited via a side-wall line patterning technique.
 2. The apparatus ofclaim 1, wherein the mill mask comprises a material capable of conformaldeposition.
 3. The apparatus of claim 1, wherein the mill mask comprisesalumina.
 4. The apparatus of claim 1, wherein the mill mask comprises aline structure with a thickness within the range of about 3 to 35 nm. 5.The apparatus of claim 1, wherein the mill mask comprises a linestructure with a thickness within the range of about 5 to 20 nm.
 6. Theapparatus of claim 1, wherein the mill mask has critical dimensionuniformity of less than about 1 nm.
 7. A read sensor comprising a readjunction between about 3 to 35 nm wide.
 8. The read sensor of claim 7,wherein the read junction is between about 5 to 20 nm wide.
 9. The readsensor of claim 7, wherein the read junction is between about 7 to 18 nmwide.